This invention relates generally to a fluid level sensing system for measuring the quantity of a medium in a storage container. More particularly, this invention relates to a level sensing arrangement for sensing and displaying the level of the medium in the container and indicating the quantity of the medium therein in terms of its level, and at a remote location.
Liquid level measuring systems and indicators therefor typically have been limited to arrangements which include a sensing element or apparatus emersed in the medium within the container. Many level gauges require that the material whose level is detected be in electrical contact with the gauge, while others require that the material be electrically conductive.
In the prior art, U.S. Pat. No. 2,868,015 discloses a level indicator for conductive liquids utilizing a plurality of vertically stacked capacitive elements arranged in a tank. The inherent drawback generally in such systems is that they are operable only with electrically conductive filler fluids which replace the fuel actually being measured, and they are potentially dangerous if the medium being measured are combustible fluids, such as gasoline, or the like. More important however, the capacitive unit disclosed in this patent must be emersed within the fluid in the tank and is unadaptable to be utilized exteriorly of the tank.
The liquid level measuring device disclosed in U.S. Pat. No. 2,751,531 also requires the sensing condenser to be emersed in the tank containing the liquid the level of which is to be sensed. The complex structure of the capacitive unit is such that it is completely incapable of use outside of the tank.
U.S. Pat. Nos. 3,010,320, 3,025,464, 3,321,971, 3,862,571 and 3,935,739 disclose level measuring devices for liquids which require electrical contact with the liquids being measured. Such devices generally suffer from the same drawbacks noted above with reference to the other patents requiring electrical contact between the mediums being measured and the various sensing probe members.
The use of an externally applied sensing device is disclosed in U.S. Pat. No. 4,165,641. That device is in the form of an inductance coil or rather a plurality of coils wound on a coil former for holding and shaping the coils. As the level of the liquid in the container rises or falls it comes into close proximity to one of the inductive coils. The electrical conduction of the liquid changes the Q of the coil thereby quenching oscillation in a detector circuit. An important ingredient in the operation of this level sensing device required the fluid, the level of which is being detected, to be conductive to some extent and therefore is only operable with limited types of material, such as at least partially conductive materials. The use of inductive coils also limit the application of this measuring means to liquid containers have coil carrying tubes.